UNUSUAL MECHANISM OF HYDROCARBON FORMATION IN THE HOUSEFLY - CYTOCHROME-P450 CONVERTS ALDEHYDE TO THE SEX-PHEROMONE COMPONENT (Z)-9-TRICOSENE AND CO2

An unusual mechanism for hydrocarbon biosynthesis is proposed from wor k examining the formation of (Z)-9-tricosene (Z9-23:Hy), the major sex pheromone component of the female housefly, Musca domestica. Incubati on of (Z)-15-[1-C-14]- and (Z)-15-[15,16-H-3(2)]tetracosenoic acid (24 :1 fatty acid) with microsomes from houseflies gave equal amounts of [ 3H]Z9-23:Hy and (CO2)-C-14. The formation of CO2 and not CO, as report ed for hydrocarbon formation in plants, animals, and microorganisms [D ennis, M. and Kolattukudy, P. E. (1992) Proc. Natl. Acad. Sci. USA 89, 5306-5310], was verified by trapping agents and by radio-GLC analysis . Incubation of (2)-15-[15,16-3H(2)] tetracosenoyl-CoA with microsomal preparations in the presence of NADPH and O-2 gave almost equal amoun ts of (Z)-15-H-3(2)]tetrasosenal (24:1 aldehyde) and Z9-23:Hy. Additio n of increasing amounts of hydroxylamine (aldehyde trapping agent) cau sed a decrease in hydrocarbon formation with a concomitant increase in oxime (aldehyde derivative) formation. The 24:1 aldehyde was efficien tly converted to (Z)-9-tricosene only in the presence of both NADPH an d O-2. Bubbling carbon monoxide (20:80 CO/O-2) or including an antibod y against housefly cytochrome P450 reductase inhibited the formation Z 9-23:Hy from 24:1 aldehyde. These data demonstrate an unusual mechanis m for hydrocarbon formation in insects in which the acyl-CoA is reduce d to the corresponding aldehyde and then carbon-1 is removed as CO2. T he requirement for NADPH and O-2 and the inhibition by CO and the anti body to cytochrome P450 reductase strongly implicate the participation of a cytochrome P450 in this reaction.